The quick and easy way to protect yourself is to contact the manufacturer and give them the serial number of the unit. They will tell you if there is a lien on the unit if they financed it. You could also find the selling dealer and ask them to check their files for any paperwork that might give you the information where to look for a lien. They will not give you any other information, but that alone is sufficient to know that you have to pay both the seller and the financial institution.
I recently purchased a piece of real estate and found that there is a Federal lien on the property by the U.S. Government for back taxes of the seller. The seller said that the taxes were paid in full many years ago, and the government agency that filed the lien has no record of it at this point. The lien is 25 years old and all records are either lost or no longer available. The government stated that it will take a while, but they will be sending a lien release to be recorded. My attorney has told me that the new Government liens expire after a certain time frame and that if the debt isn't paid by then, that they will either file a new lien or they will abandon it as noncollectable. Back when this lien was paid off, a release of lien was sent to the debtor, but he never recorded it. When I paid off my mortgage, I had to record the release of lien. Usually, it is up to the owner of the property to record the release of the lien, because there is a fee involved in most instances and the person holding the lien, doesn't want to pay it.